Various different types of masks are used to provide fresh air or oxygen to the airways of humans. A specialised category of masks is used to provide positive pressure to the human airway. Positive pressure applied in this manner has two different goals.
In a first category, positive pressure is applied to the lungs for the purpose of stabilising the lungs, and in particular for maintaining a minimum inflation level of the small air spaces in which gas transfer occurs (the alveoli). This therapy is very useful in patients with a variety of lung diseases, where the disease process tend to lead to collapse (closure of the airway containing regions of the lung).
In a second category, the positive pressure is applied to the nasal airway with the intention of maintaining the pressure in, and the patency of, the upper airway. This form of positive airway pressure is known as nasal continuous positive airway pressure (nasal CPAP). This is now the “gold standard” treatment for the condition known as obstructive sleep apnea (OSA), and also for snoring. Obstructive sleep apnea is a condition in which the upper airway closes in sleep, and does so repeatedly. Nasal CPAP, when applied for the duration of sleep, stabilises the upper airway and allows for normal sleep and normal breathing.
Masks for applying nasal CPAP, or nasal pressure support ventilation have a requirement to be able to deliver pressure and flow and maintain pressures within the mask without permitting leaks. Leaks are undesirable as they can allow the pressure in the mask to drop below a therapeutic level. Leaks may also be an irritation particularly, if the leak causes jets of air/oxygen to be directed into the patient's eye. Leaks interrupt a patient's sleep which is undesirable as interrupted sleep is known to be of much less value than uninterrupted sleep. Further, as the masks are for use during natural sleep, a high level of comfort in the fit of the mask is necessary.
One very common mask design includes three separate components as follows:                1. A soft mouldable rubberised interface which comes in direct contact with the patient's facial skin.        2. A rigid manifold to which the soft interface is connected, and which covers the patient's nose. The manifold includes:                    a) connector lugs to which straps from a harness are connected;            b) connections to an air delivery pipe; and            c) a number of relatively small holes or equivalent feature to provide a controlled leak of air to the atmosphere.                        3. A harness which goes around the head from which three or more straps extend to connect to the lugs on the rigid manifold.        
A seal is achieved by the mask being pulled onto the face by the straps attached to the rigid manifold. The seal is achieved by the rim of the mask coming into contact with the skin. In this way, direct force is applied via the straps (harnessed place around the head), and transmitted through the rigid manifold. There are a number of disadvantages with this mask which are discussed in more detail below following a description of other, known mask types.
More recently, in order to achieve a good seal “bubble” type gas delivery masks have been developed. One such mask is described in Australian Patent No. 643994, dated 16 May 1991. The mask described therein has a face contacting portion which is formed from an elastomeric material and is shaped to define a large bubble or dome shaped chamber. When gas is delivered through the chamber, the chamber tends to balloon outwardly and, when fitted to a patient, the face contacting portion is caused to overly a region of the patient's face and seal three dimensionally with the contours of the overlaid facial region. For practical reasons the mask is integrated with a rigid shell-like moulding which does not contact the patient's face. The shell is provided to enable a gas supply line to be connected to the mask, to facilitate fastening of the mask to a patient's face and to minimise the risk that movement of the gas supply line will disrupt the seal between the mask and the patient's face.
Other earlier masks comprise a shell custom moulded to fit around the individual nose for each patient, and either use a glue, or alternatively a soft inner part against which a tight fit is achieved. Once again, this type of mask may be held in place by straps and a head harness attached to the hard shell.
The main problems when designing a mask is that the mask must be able to achieve an air tight seal with the subject's face and at the same time be sufficiently comfortable to be able to be worn for hours without causing discomfort to the subject and in particular to allow the subject to sleep.
Movement of the head, and subsequent dislodgment of the mask, and breakage of the seal are major problems with prior art masks. This is a particular problem when a patient lies on their side, with the side of their head on the pillow as the rigid manifold tends to contact the pillow The contact moves the manifold relative to the patient's face, is transmitted to, and affects the integrity of the seal and also the manifold can be pushed onto the patient's nose causing discomfort to the patient.
Using the first type of mask as described above, which includes the three separate components, seal breakage is addressed by pulling the straps firm. This however, can lead to discomfort for the patient.
In the second mask type described above (the “bubble type mask”), the bubble provides a continuous rolling seal, so that minor head and other movements are accommodated within the excess thin membrane. However, large head movements may not be accommodated by the rolling seal.
A major problem for all masks is that an air delivery pipe must be attached to the mask at some point. Movement of the head and the pipe leads to torsion which is transmitted through the hard shell of the manifold and can cause the sealing margins of the mask to rise up and allow a leak. The above-referenced “bubble mask” patent, (Australian patent No 634994), tries to address this by having a “universal joint” between the air delivery pipe and the rigid manifold. Australian Patent No 684412, by the same inventor as the earlier Australian patent No 634994, addresses this problem by making a portion of the wall containing the gas supply port exhibit a degree of flexibility that is greater than that of adjacent regions of the mask so that movement by the connecting gas supply line will be accommodated at least in part by flexing of the wall portion. Whilst both masks produce relatively satisfactory seals they are quite bulky, relatively heavy and ungainly.
In existing masks, because the straps must anchor onto a rigid point, they are attached to the rigid manifold; the result is that typically the strap leaves the side of the face near the cheeks, and passes through air until it reaches the lug on the manifold. This “floating” part of the strap, provides a significant weakness and adversely affects the integrity of the seal when the patient's head moves When the subject rolls onto their side, this floating part of the strap is easily distorted, and pulls on the mask and leads to a leak.
In one aspect, the present invention seeks to provide an improved mask which reduces the relative size, weight and bulk of the existing masks and yet provides a satisfactory seal.
A variant of the mask may be used to supply treated air, oxygen or an air/oxygen blend or the like to patients. In a known technique such treated air is supplied from a pipe located near a patient's nasal airway and the flow of air is directed past the patient's nares. Thus, in a related aspect the present invention seeks also to provide harness for supporting a pipe for supplying a flow of gas to a patients nasal airway.